The combination of ferrocene (Fe(C5H5)2) and carbon dioxide has been shown to be a superb flame retardant. In this combination, the ferrocene appears to quench free radicals that propagate the flames by decomposing into naked iron atoms, and an inert gas such as CO2 enhances this effect by preventing the atomic iron from being trapped by oxygen extending the compositions efficacy.
Free ferrocene is not generally useful as a fire retardant alone, because it has a low melting point of 174° C. and boiling point of 249° C.; and even before melting, ferrocene can sublime to get into the gas phase. Thus, a number of attempts have been made to conjugate ferrocene to a polymer backbone to impart fireretardant properties on the polymer. However, ferrocene interferes with the properties' polymer such as coating ability, rheology, color, etc.; and the cost of synthesizing a ferrocene polymer conjugate increased production costs of such polymers. Moreover, even with minor heating, polymer-based coatings can become contaminated with free ferrocene molecules, and ferrocene can leach out from the system into the environment. In order to avoid these problems, ferrocene molecules need to be released into the gas phase only at fairly high temperatures. A potential solution to this problem is encapsulating ferrocene in a sol-gel matrix.